The present invention relates to vehicle parts, and particularly to an engaging device for a starter and a starter including the engaging device.
A starter is also referred to as a motor, in which power is generated by a DC motor and then is transmitted to a flywheel gear via a starter gear. A flywheel is driven, rotating a crankshaft to start an engine.
After the starter is activated, a pinion is moved axially along a main shaft. The teeth of the pinion are elastically pressed against the teeth of a ring gear. Then, the pinion is rotated along with the main shaft, such that the teeth of the pinion slide into tooth spaces of the ring gear, and thus engaging of the pinion and the ring gear is achieved.
In most cases, the pinion of the starter may not engage with the ring gear directly. The engaging motion will not begin until the pinion is driven by the electric motor to turn a certain angle. The engaging process of the pinion requires some time and the engagement depth increases with time. Since there is a very high torque when the electric motor just starts to rotate (when the speed is low), generally, at the time when the pinion is driven by the electric motor to turn a certain angle to find the tooth space of the gear ring, the pinion still cannot engage with the ring gear completely, to put it more precisely, the engagement depth in the ring gear (initial engagement depth) is very small (typically 0.5-1.5 mm). Under high torque, there is a possibility that the ring gear will be scratched by the pinion if the engagement depth of the pinion is too small (typically, the strength of the material of the pinion is much higher than that of the ring gear, and so is the rigidity). This phenomenon is similar to the process of machining a part with a milling cutter and thus is commonly known as “teeth milling”. Therefore, the initial engagement depth of the pinion with the ring gear is an important factor to judge the engagement performance of a starter.
Currently, there are a few solutions to improve the engagement performance. One of them is to produce a tip chamfer for the pinion and a flank chamfer for the ring gear at the opposing end surfaces of the pinion and the ring gear, to facilitate guiding the teeth of the pinion to slide along the teeth of the ring gear. However, a large relative rotating angle is still needed for the pinion to engage with the ring gear, and the need to rely on motor drive to implement the process of finding tooth spaces cannot be avoided completely. Another solution is, by using a two-stage circuit, to allow an enhanced first stage circuit to drive the pinion to fulfill the process of finding tooth spaces and engaging, a second stage current to actually drive an engine is not switched on until the engagement depth of the pinion reaches a relatively high value (over 5 mm), thereby reducing teeth milling phenomenon during the engaging process caused by driving a pinion under high torque. However, another circuit design is needed to achieve this function and thus increases the cost of the product. Further, such a circuit is prone to failure in poor working conditions, causing dissatisfaction from a user.